One-piece semi-rigid electrical contact

ABSTRACT

An electrical contact includes a hollow tube having first and second end portions and a center portion; and a spring portion formed in a wall of the hollow tube. The spring portion may be located in the center portion of said hollow tube or in one of the first and second end portions of the hollow tube. The spring portion may be a helical spring portion and may include two helical portions wound in opposite directions. At least one of the first and second end portions may have a diameter that is less than a diameter of said center portion. At least one of the first and second end portions may have a hemispherical shape or closed end. The hollow tube may be of a metal such as stainless steel or may be a hollow tube coated with an electrically conductive material such as one of copper, silver, or gold. The contact may have a shoulder having a diameter which is greater than the diameter of at least one of the first and second end portions and said center portion of the tube and may be disposed between one of the first and second end portions and the center portion of the tube or in one of the first and second end portions or the center portion of the tube.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrical contacts and moreparticularly to a one-piece semi-rigid electrical contact with anintegral compression spring for use in solderless high-speed electricalconnectors, that is, electrical connectors capable of operating in thefrequency range of from less than 1 GHz to 20 GHz.

2. Description of the Related Art

Conventionally, an electrical connector for use with printed circuitboards, for example, contained a plurality of solder pins for solderingto the printed circuit board. While this is still used in manyapplications, in the case of connectors for use in high-speedapplications, particularly when it is desirable to have a connector withvery close pin spacing to reduce its size, it has been found thatsoldering such a connector to a printed circuit board becomes verycostly in that it is impossible to visually locate a short or groundbetween the connector and the printed circuit board. An expensive x-raytechnique must often be used to inspect the connections since the solderpins are hidden under the connector. Furthermore, the increasing numberof pins needed in such connectors make the soldering of such connectorsto printed circuit boards more difficult, thereby reducing theproduction yield and accordingly increasing production costs.

Still furthermore, there are presently significant uses for compactelectrical connectors, capable of operating in the frequency range offrom less than 1 GHz to 20 GHz, and having large numbers of coaxial ortwinaxial interconnections. Conventional electrical connectors are justnot suitable for such applications.

In view of the problems noted above, attempts have been made to utilizesolderless electrical connectors having some form of resilient contactsused to connect the electrical connector to the printed circuit board.For example, U.S. Pat. No. 6,386,890 to Bhatt et al. discloses a printedcircuit board to module mounting and interconnecting structure andmethod. As illustrated in FIG. 3 thereof, a resilient conductor 52 to isused to connect a contact 34 to a contact 40. The conductor 52, as notedin column 5 thereof, may be a “fuzzy button” connector similar to thoseproduced by Cinch Inc. Alternatively, the conductor 52 may be a platedelastomeric member, a precious metal plated wire or a stamped metalcontact with precious metal plating. As further noted therein, it ispreferable that the precious metal wire used for the conductor 52 have arandom orientation to provide multiple contact points on the contacts 40and 34, thereby increasing the reliability of the overall electricalconnection by providing multiple hertzian contacts.

Unfortunately, the resilient contacts of Bhatt et al. have proven to besomewhat fragile in that they can be easily destroyed if they brush upagainst a hard surface. Furthermore, they are very expensive to produceand are very difficult to install in the electrical connector, therebyincreasing production costs.

On the other hand, U.S. Pat. No. 6,341,962 to Sinclair discloses asolderless grid array connector that utilizes helical wound springcontacts to make solderless connections between an electrical connectorand a printed circuit board. While such spring contacts are animprovement over the resilient contacts of Bhatt et al., they are verydifficult to manufacture, particularly in the case of spring contactshaving very small dimensions.

Furthermore, as noted above, electrical contacts are needed for use inan electrical connector to work with high frequency pulse or analogsystems, that is, for use in a frequency range of from less than 1 GHzto at least 20 GHz .The electronic properties are critical. That is, theimpedance of the electrical connector requires that the capacitivereactance be controlled, the inductive reactance be controlled and theresistance value be controlled. The overall performance depends on aspecific impedance Zo, (i.e., such as 50 ohms, 75 ohms, etc.) needed tomaintain a minimum insertion loss and minimum reflections of the chargeslaunched in electronic circuits, over the bandwith in use. Thedimensions of the connectors are critical to ensuring a minimum ofelectronic disturbance and to minimize any crosstalk between adjacentchannels. These electrical connectors may be used for coaxial/twinaxialand transmission line systems on motherboard to daughterboard withhigh-speed processors. The simple spring arrangement of Sinclair doesnot work at these high frequencies.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a one-piece semi-rigid electrical contact with an integralcompression spring for use in solderless high-speed electricalconnectors.

These and other objects of the present invention may be achieved byproviding an electrical contact comprising: a hollow tube having firstand second end portions and a center portion; and a spring portionformed in a wall of said hollow tube.

The spring portion may be a helical spring portion and may be located inone of the first and second end portions or the center portion.

The helical spring portion may include turns wound in a first directionand turns wound in a second direction opposite that of the firstdirection.

At least one of said first and second end portions may have a diameterthat is less than a diameter of said center portion and at least one ofsaid first and second end portions may have a hemispherical shape or aclosed end.

The hollow tube may be of a metal such as stainless steel or may be ahollow tube coated with an electrically conductive material such ascopper, silver, or gold.

The contact may have a shoulder having a diameter that is greater thanthe diameter of at least one of said first and second end portions andsaid center portion of the tube.

The shoulder may be disposed between one of said first and second endportions and said center portion of the tube.

The shoulder may be disposed in one of said first and second endportions of the tube or in said center portion of the tube.

These and other objects of the present invention may also be achieved byproviding a method of fabricating and electrical contact, the methodcomprising: forming a hollow tube having first and second end portionsand a center portion; and forming a spring portion in a wall of thehollow tube.

The spring portion may be formed in the center portion of the hollowtube or in one of the first and second end portions of the hollow tube.

The spring portion may be formed as a helical spring portion and thespring portion may be formed with one of a cutting process, an etchingprocess, and a laser cutting process.

The spring portion may have turns wound in a first direction and turnswound in a second direction opposite that of the first direction.

At least one of the first and second end portions may be formed with adiameter that is less than a diameter of the center portion.

At least one of the first and second end portions may be formed so as tohave a hemispherical shape.

At least one of the first and second end portions may be formed so as tohave a closed end.

The hollow tube may be formed of a metal such as stainless steel.

The hollow tube may be formed of a hollow tube coated with anelectrically conductive material such as one of copper, silver, or gold.

A shoulder may be formed having a diameter that is greater than thediameter of at least one of the first and second end portions and thecenter portion of the tube.

The shoulder may be formed between one of the first and second endportions and the center portion of the tube or in one of the first andsecond end portions of the tube or in the center portion of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and a better understanding of the present invention willbecome apparent from the following detailed description of an exampleembodiment and the claims when read in connection with the accompanyingdrawings, all forming a part of the disclosure of this invention. Whilethe foregoing and following written and illustrated disclosure focuseson disclosing an example embodiment of the invention, it should beclearly understood that the same is by way of illustration and exampleonly and that the invention is not limited thereto. This spirit andscope of the present invention are limited only by the terms of theappended claims.

FIG. 1 is a view of one example of an embodiment of an electricalcontact in accordance with the present invention.

FIG. 2 is a view of another example of an embodiment of an electricalcontact in accordance with the present invention.

FIG. 3 is a view of yet another example of an embodiment of anelectrical contact in accordance with the present invention.

FIG. 4 is a view of still another example of an embodiment of anelectrical contact in accordance with the present invention.

DETAILED DESCRIPTION

Before beginning a detailed description of the subject invention,mention of the following is in order. When appropriate, like referencenumerals and characters may be used to designate identical,corresponding, or similar components in differing drawing figures.Furthermore, in the detailed description to follow, examplesizes/models/value/ranges may be given, although the present inventionis not limited thereto. When specific details are set forth in order todescribe example embodiment of the invention, it should be apparent toone skilled in the art that the invention can be practiced without, orwith variations of, these specific details.

FIG. 1 is a view of one example of an embodiment of an electricalcontact in accordance with the present invention. The illustratedelectrical contact 100 has a tubular shape with open ends and a helicalportion 120 located between the ends. As an example of the dimensions ofsuch a contact, the length of the contact 100 may be on the order of 0.2inches and the diameter of the contact may be on the order of 0.025inches and the wall thickness of the contact may be on the order of0.008 inches. Such dimensions allow the electrical contact 100 to beused in very high frequency applications in multipin surface mountelectrical connectors having very close pin spacings.

There are several parameters that must be considered in designing suchan electrical contact. That is, if the electrical contact is to be usedin an electrical connector at a specified frequency range and impedance,it is necessary to control the capacitive reactance, and inductivereactance, and resistance value of the electrical contact. In addition,the contact spacing of the connector determines the maximum diameter ofthe electrical contact and the configuration of the electrical connectordetermines the length of the electrical contact. Furthermore, themechanical spring force caused by the helical spring portion of theelectrical contact must be specified in accordance with the requirementsof the electrical connector.

To control the above-noted parameters, the length, diameter, wallthickness, length and pitch and slot width of the helical portion of theelectrical contact, and material or materials used in the electricalcontact can be adjusted. For example, the electrical contact 100 can befabricated of stainless steel which may be electroplated inside and outwith nickel, copper, gold, or silver to keep its electrical resistancevalue relatively low. Other metals may also be used for both theelectrical contact and its plating material. The length and diameter ofthe electrical contact 100 would normally be determined by the connectorconfiguration (that is, pin spacing and interposer thickness). Themechanical spring force and electrical reactances would determine thewall thickness, length and pitch and slot width of the helical portionof the electrical contact. The calculation of the various dimensions ofthe electrical contact 100 are well known to those skilled in the artand have been omitted for the sake of brevity.

The electrical contact 100 of FIG. 1 may be fabricated by first forminga tube of the desired material and diameter and wall thickness and bythen cutting the tube to the proper length. If electroplating or otherplating or coating techniques are needed to plate the tube with a secondmaterial, either inside or outside the tube or both inside and outsidethe tube, such plating can be performed before or after cutting the tubeto its proper length or subsequent to further fabrication steps.

The helix portion of the electrical contact 100 would then be formed inthe tube by any suitable means, such as laser cutting, or any other finecutting or etching or similar process. The resultant electrical contact100 would then be inserted into an aperture of an interposer of anelectrical connector, such as the electrical connector disclosed in thecopending U.S. patent application Ser. No. 10,234,859, entitledInterconnection System, filed concurrently with the present applicationand having a common Assignee.

One problem with the electrical contact 100 of FIG. 1 is the fact thatits diameter is constant, such that there is nothing to prevent theelectrical contact 100 from falling out of its aperture in theinterposer of the electrical connector prior to its assembly. In somecases, an epoxy dot may be disposed on an outside wall of the electricalcontact 100 to retain the electrical contact 100 in its aperture.Alternatively, the configuration of the electrical contact 100 can bemodified so as to be as shown in FIG. 2.

The electrical contact 200 of FIG. 2 differs from the electrical contact100 of FIG. 1 in several respects. Namely, the helical spring portion220 of the electrical contact 200 is located on one end 250 thereofrather than being located in a central portion thereof. Furthermore, areduced portion 230 of the electrical contact 200 has a reduced diameterin comparison to the helical spring portion 220, with a shoulder 235being disposed therebetween. Still furthermore, the end portion 240 ofthe reduced portion 230 has been formed into a hemispherical shape. Thisfacilitates better electrical contact with its mating contact point incertain cases. While the end portion 240 is open, it could also beformed so as to have a closed end. In addition, the end portion 240could be formed so as to have a conical shape or so as to have a flatend. Still furthermore, the end portion 240 can be formed so as to haveone or more points or serrations so as to facilitate better electricalcontact with its mating contact point. It is to be noted that such anend portion 240 may be used with surface mount electrical connectors.

By forming the electrical contact 200 of FIG. 2 with the reduced portion230, the electrical contact 200 can be prevented from falling throughits respective aperture in its respective interposer by merely ensuringthat the respective aperture has a diameter which is greater than thatof the reduced portion 230 but less than that of the helical springportion 220.

Alternatively, the configuration of the electrical contact 100 of FIG. 1can also be modified so as to be as shown in FIG. 3. Namely, theconnector 300 of FIG. 3 differs from that of the connector 100 of FIG. 1in that a shoulder 330 has been added. The shoulder 330 has beenprovided to prevent the electrical contact 300 from falling through itsrespective aperture in its respective interposer provided that therespective aperture has a diameter which is greater than that of thehelical spring portion 320 of the electrical contact 300 but less thanthat of the shoulder 330 of the electrical contact 300.

FIG. 4 is a view of still another example of an embodiment of anelectrical contact in accordance with the present invention. In FIG. 4,the electrical contact 400 is similar to the electrical contact 100 ofFIG. 1 with the exception of the helical portion 410 of the contact 400being divided into two portions, namely, a first portion of 420 havingturns wound in a first direction and a second portion 430 having turnswound in a second opposite direction. The use of such a helical portion410 having turns in opposite directions results in a reduced inductivereactance for the electrical contact 400.

This concludes the description of the example embodiment. Although thepresent invention has been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis invention. More particularly, reasonable variations andmodifications are possible in the component parts and/or arrangements ofthe subject combination arrangements within the scope of the foregoingdisclosure, the drawings, and the appended claims without departing fromthe spirit of the invention. In additions to variations andmodifications in the component parts and/or arrangements, alternativeuses will also be apparent to those skilled in the art.

For example, while the illustrative examples discussed above includeelectrical contacts having a circular cross-section, the presentinvention is not limited to electrical contacts having circularcross-sections but rather includes electrical contacts having othercross-sections, such as oval cross-sections, for example. Furthermore,while the electrical contacts discussed above are indicated as beingformed of metal, the present invention is not limited thereto in thatthere are presently available processes to coat an object formed of anon-conducting material, such as a plastic, so as to make itelectrically conductive. Still furthermore, in a multi-pin connectorutilizing the electrical contacts of the present invention, the windingdirection of the helical spring portions of adjacent electrical contactscan be opposite each other so as to reduce any mutual inductancetherebetween. Lastly, the electrical contacts of the present inventionare not limited to the specific shapes illustrated in the drawingfigures. That is, while a helical spring portion has been illustratedfor all of the electrical contacts in the drawing figures, the presentinvention is not limited thereto in that shapes other than helical (suchas serpentine) may be utilized in forming the spring portion of theelectrical contacts.

What is claimed is:
 1. An electrical contact comprising: a hollow tubehaving first and second end portions and a center portion, at least oneof said portions comprising a hollow rigid solid wall tube portion; anda spring portion formed as a wall of one of said portions of said hollowtube.
 2. The contact of claim 1, wherein said spring portion is locatedin said center portion of said hollow tube.
 3. The contact of claim 2,wherein said spring portion comprises a helical spring portion.
 4. Thecontact of claim 2, wherein said spring portion comprises a helicalspring portion including turns wound in a first direction and turnswound in a second direction opposite that of said first direction. 5.The contact of claim 1, wherein said spring portion is located in one ofsaid first and second end portions of said hollow tube.
 6. The contactof claim 5, wherein said spring portion comprises a helical springportion.
 7. The contact of claim 5, wherein said spring portioncomprises a helical spring portion including turns wound in a firstdirection and turns wound in a second direction opposite that of saidfirst direction.
 8. The contact of claim 1, wherein said spring portioncomprises a helical spring portion.
 9. The contact of claim 1, whereinat least one of said first and second end portions has a diameter thatis less than a diameter of said center portion.
 10. The contact of claim1, wherein at least one of said first and second end portions has ahemispherical shape.
 11. The contact of claim 1, wherein at least one ofsaid first and second end portions has a closed end.
 12. The contact ofclaim 1, wherein said hollow tube comprises a metal.
 13. The contact ofclaim 12, wherein said metal comprises stainless steel.
 14. The contactof claim 1, wherein said hollow tube comprises a hollow tube coated withan electrically conductive material.
 15. The contact of claim 1, whereinsaid hollow tube comprises a hollow tube coated with one of copper,silver, or gold.
 16. The contact of claim 1, further comprising ashoulder having a diameter which is greater than a largest diameter ofat least one of said first and second end portions and said centerportion of said hollow tube.
 17. The contact of claim 16, wherein saidshoulder is disposed between one of said first and second end portionsand said center portion of said hollow tube.
 18. The contact of claim16, wherein said shoulder is disposed in one of said first and secondend portions of said hollow tube.
 19. The contact of claim 16, whereinsaid shoulder is disposed in said center portion of said hollow tube.20. The contact of claim 1, wherein said spring portion comprises ahelical spring portion including turns wound in a first direction andturns wound in a second direction opposite that of said first direction.21. An electrical contact comprising: a hollow tube having first andsecond end portions and a center portion; and a spring portion formed ina wall of said hollow tube; wherein said spring portion comprises ahelical spring portion including turns wound in a first direction andturns wound in a second direction opposite that of said first direction.22. The contact of claim 21, wherein said spring portion is located insaid center portion of said hollow tube.
 23. The contact of claim 21,wherein said spring portion is located in one of said first and secondend portions of said hollow tube.
 24. The contact of claim 21, whereinat least one of said first and second end portions has a diameter thatis less than a diameter of said center portion.
 25. The contact of claim21, wherein at least one of said first and second end portions has ahemispherical shape.
 26. The contact of claim 21, wherein at least oneof said first and second end portions has a closed end.
 27. The contactof claim 21, wherein said hollow tube comprises a metal.
 28. The contactof claim 27, wherein said metal comprises stainless steel.
 29. Thecontact of claim 21, wherein said hollow tube comprises a hollow tubecoated with an electrically conductive material.
 30. The contact ofclaim 21, wherein said hollow tube comprises a hollow tube coated withone of copper, silver, or gold.
 31. The contact of claim 21, furthercomprising a shoulder having a diameter which is greater than a largestdiameter of at least one of said first and second end portions and saidcenter portion of said hollow tube.
 32. The contact of claim 31, whereinsaid shoulder is disposed between one of said first and second endportions and said center portion of said hollow tube.
 33. The contact ofclaim 31, wherein said shoulder is disposed in one of said first andsecond end portions of said hollow tube.
 34. The contact of claim 31,wherein said shoulder is disposed in said center portion of said hollowtube.